1. Field of the Invention
The invention relates to a motor control apparatus and an image forming apparatus using it.
2. Related Background Art
In an apparatus using a motor as a driving source, generally, it is required that a driving member which is driven by the motor is repetitively operated while keeping a predetermined precision level. Particularly, in an image forming apparatus in an electrophotographic system, to form an image of high precision, it is required to use a motor having higher rotating precision as a motor for driving a photosensitive member or for driving a transfer member. To accomplish such an object, an ultrasonic motor is used as a motor for driving the photosensitive member or for driving the transfer member.
The ultrasonic motor, is a motor using an ultrasonic vibration, proposed by JP-A-58-14682. As described in detail in JP-A-63-1379, JP-A-60-176470, JP-A-59-204477, or the like with respect to the driving of such a motor, a stable rotating performance of a constant speed is realized by periodically adjusting the drive frequency or the driving voltage and the pulse width of the driving voltage in accordance with a signal of speed detecting means, such as an encoder signal or the like.
On the other hand, abrasion of the motor of the apparatus and motor driving members, due to their use over a long period of time, which is caused by the occurrence of friction between the members when the motor of the apparatus and the motor driving members which are driven by the motor are made operative, is unavoidable. Even if a motor having high precision driving characteristics, such as an ultrasonic motor is used, such abrasion is not exceptional. Therefore, hitherto, when the abrasion of the motor driving members progresses and a stable constant speed rotation at a target speed in the stationary state becomes impossible, a countermeasure, such as replacement, reparation, or the like, by a serviceman or the like, is performed.
However, in the conventional motor control apparatus as mentioned above, the stable driving of the apparatus main body becomes disabled for a period of time until a countermeasure, such as replacement, reparation, or the like, by a serviceman or the like is performed after the stable rotation of the motor driving members becomes impossible due to the abrasion of the members. Particularly, in the case of an image forming apparatus having such a motor control apparatus, high quality image formation cannot be performed for such a period of time. It is therefore impossible to meet a requirement by the operator to form an image in urgent for the period of time until a countermeasure, such as replacement, reparation, or the like by a serviceman, is performed.
In an image forming apparatus for a business use or the like in which it is required that the apparatus always operates without a halt, there is a problem such that the usefulness of the apparatus is diminished due to the occurrence of the inoperative time.